The energy capacity of lithium ion secondary cells is much greater than that of lead, nickel-cadmium, or nickel-metalhydride cells.
As a result, a particularly advantageous application thereof lies in making batteries for mobile telephones.
Such lithium ion secondary cells comprise an electrolyte that conducts lithium ions sandwiched between a positive electrode and a negative electrode.
By way of example, the negative electrode material may be lithium itself, an insertion compound of lithium in carbon, or an oxide suitable for inserting lithium. In the latter two cases, such cells are said to be "rocking-chair" cells.
The electrolyte that conducts lithium ions may either be a liquid or a solid, in general of the polymer type, in which there is dissolved a lithium salt that is capable of ionizing to produce lithium ions.
The positive electrode is constituted by an oxide capable of inserting lithium reversibly.
By way of example, mention may be made of oxides having the following formulae LiNiO.sub.2 and LiCoO.sub.2, and derivatives thereof, which are presently in use in commercially-available batteries; for example, mention may be made of the "lithium-ion" battery which makes use of the LiCoO.sub.2 oxide coupled with the compound Li.sub.x C.
Also, proposals have already been made to use lithium and manganese double oxides having the general formula Li.sub.x Mn.sub.y O.sub.z in which the values of x, y, and z are such that the composition of the oxide is close to LiMn.sub.2 O.sub.4, for use as a positive electrode material.
Industrially, the advantage of this oxide is that it contains manganese which is considerably less expensive than nickel or cobalt, thereby giving rise to higher performance batteries at lower cost.
Various methods are already known for preparing the lithium and manganese double oxide of formula Li.sub.x Mn.sub.y O.sub.z.
For example, mention can be made of a solid state method of synthesizing lithium and manganese double oxide from MnO.sub.2 or Mn.sub.3 O.sub.4 and various lithium salts such as the carbonate, the nitrate, and the hydroxide.
Another known method of synthesizing lithium and manganese double oxide is based on pyrolyzing precipitates obtained from manganese acetate and lithium acetate or carbonate.
In addition, a method is known in which lithium and manganese double oxide is synthesized in the form of a film from targets of LiMn.sub.2 O.sub.4.
Finally, a method of synthesis is known in which a lithium and manganese polymer complex is formed, and the LiMn.sub.2 O.sub.4 oxide is obtained by pyrolyzing the complex. In that method, the polymer acts only as a supporting matrix to avoid particles agglomerating, and not at all as a catalyst for the explosive formation of a lithium and manganese double oxide is formed by an explosive reaction.
The above-mentioned methods are explained more particularly in the following publications:
J. M. Tarascon and D. Guyomard, "Li metal-Free rechargeable batteries based on Li.sub.1+x Mn.sub.2 O.sub.4 cathode (0.ltoreq.x.ltoreq.1) and carbon anodes", J. Electrochem. Soc., Vol. 138, No. 10, October 1991, pp. 2864-2868; PA1 A. Momchilov et al., "Rechargeable lithium battery with spinel-related MnO.sub.2. II. Optimization of the LiMn.sub.2 O.sub.4 synthesis conditions", J. of Power Sources, 41 (1993), pp. 305-314; PA1 Quingzhong Xu and Guoxiang Wan, "Rechargeable Li/LiMn.sub.2 O.sub.4 batteries with a polymeric solid electrolyte", Journal of Power Sources, 41 (1993), pp. 315-320; PA1 Yvan Gao and J. R. Dahn, "Thermogravimetric analysis to determine the lithium to manganese atomic ratio in Li.sub.1+x Mn.sub.2-x O.sub.4 ", App. Phys. Lett., 66 (19), May 8, 1995, pp. 2487-2489; PA1 S. R. Sahaya Prabaharan et al., "Bulk synthesis of submicrometer powders of LiMn.sub.2 O.sub.4 for secondary lithium batteries", J. Mater. Chem., 1995.5 (7), pp. 1035-1037; PA1 K. H. Hwang et al., "Fabrication and characterization of an Li--Mn--O thin film cathode for rechargeable lithium microbatteries", J. of Power Sources, 54 (1995), pp. 224-227; PA1 K. Kanamura et al., "Structural change of the LiMn.sub.2 O.sub.4 spinel structure induced by extraction of lithium", J. Mater. Chem., 1996, 6 (1), pp. 33-36; PA1 W. Liu et al., "Synthesis and electrochemical studies of spinel phase LiMn.sub.2 O.sub.4 cathode materials prepared by the Pechini process", J. Electrochem. Soc., Vol. 143, No. 3, March 1996, pp. 879-884; PA1 JP 07142065, HAYAHI YASUSHI, "Manufacture of active material for lithium secondary battery"; PA1 WO 96 22 943; and PA1 FR 2 628 664. PA1 a) a polymer complex of lithium and of manganese is prepared in the form of a gel or of a xerogel by causing a reducing polymer, copolymer or polymer mixture possessing complexing functions for lithium and manganese to react in a common solvent with an oxidizing lithium salt and with an oxidizing manganese salt, and by evaporating off the solvent, partially or in full; and PA1 b) the resulting lithium and manganese polymer complex is mineralized by the explosive oxidation-reduction technique to recover fine amorphous particles of the oxide of formula Li.sub.x Mn.sub.y O.sub.z. PA1 a) a lithium and manganese polymer complex is made in the form of a gel by causing a polymer, a copolymer, or a mixture of polymers possessing complexing functions for lithium and for manganese to react in a common solvent with a lithium salt and with a manganese salt, and by evaporating off part of the solvent; PA1 b) a metal support is impregnated with the resulting lithium and manganese polymer complex gel to which finely divided carbon has been added; PA1 c) said impregnated support is dried; and PA1 d) said impregnated support is mineralized under conditions such that the carbon and the metal support are not themselves oxidized. PA1 a) a lithium and manganese polymer complex is made in the form of a gel by causing a polymer, a copolymer, or a mixture of polymers possessing complexing functions for lithium and for manganese to react in a common solvent with a lithium salt and a manganese salt, and by evaporating off part of the solvent; PA1 b) a support such as a carbon felt or cloth of very high specific surface area is impregnated with the resulting lithium and manganese polymer complex gel; and PA1 c) the impregnated support is mineralized at a temperature not less than 350.degree. C. under an appropriate atmosphere.